The present invention relates to a reversible expansion valve having a one way check valve mechanism which allows the valve to operate stably whether the flow direction of a fluid such as a refrigerant may be forward or reverse. An expansion valve according to the present invention closes the check valve when a fluid flows in the forward direction and operates in the same way as a conventional expansion valve of one-way type. However, the check valve in the art will be opened when the fluid flow is reversed to release a pressure which has entered a bimetal chamber of the valve to the low pressure side thereby ensuring a reverse mode of operation without a pressure increase in the bimetal chamber or accumulation of the fluid in the chamber. In this way, however, no specific means is provided to prevent the fluid from entering the bimetal chamber. Moreover, the discharge of fluid once accumulated in the bimetal chamber is performed only when the fluid flow is in one of the two directions.